Police are treating the case of the 9-year-old boy found with head injuries 15km outside of Timaru as an abduction.

The boy, who was discovered in a distressed state at Holme Station Bridge on Thursday afternoon, is in Timaru Hospital in a stable condition but has not been able to speak to police. His family are with him.

Police are urging witnesses to come forward with any information about his suspected abduction.

The boy left Oceanview Heights School on Selwyn St at about 3pm and was found at the bridge at 4.20pm.

He is described as being of dark complexion, slim build, approximately 30kg with dark hair. He is considered small for his age and police describe his height as more like that of a 6 or 7-year-old.

He was wearing an Oceanview Heights School uniform - a dark blue polar fleece, dark blue shorts and a teal green polo shirt.

Detective Sergeant Dylan Murray confirmed a specialist search team from Christchurch had been at the site at the weekend but would not say whether they had uncovered anything.